Archaeoindris fontoynontii is an extinct giant lemur and the largest primate known to have evolved on Madagascar, comparable in size to a male gorilla. It belonged to a family of extinct lemurs known as "sloth lemurs" (Palaeopropithecidae) and, because of its extremely large size, it has been compared to the ground sloths that once roamed North and South America. It was most closely related to Palaeopropithecus, the second largest type of sloth lemur. Along with the other sloth lemurs, Archaeoindris was related to the living indri, sifakas, and woolly lemurs, as well as the recently extinct monkey lemurs (Archaeolemuridae). The genus, Archaeoindris, translates to "ancient indri-like lemur", even though it probably became extinct recently, around 350 BCE.
Archaeoindris was first described by Herbert F. Standing in 1909 on the basis of subfossil fragmentary jaws, although Charles Lamberton later discovered a complete skull. Only six bones from the lower skeleton have been found and excavations in the 1980s offered no leads for new finds. Its remains have been found at only one location: Ampasambazimba, a subfossil site in central Madagascar. Following its initial discovery, some subfossil remains of Megaladapis grandidieri (a type of extinct koala lemur) were mistakenly associated with Archaeoindris, while smaller leg bones from a juvenile and a massive adult leg bone were erroneously assumed to belong to two separate species. These errors were gradually corrected between the 1930s and 1980s.
The skeleton of Archaeoindris was massive and robust, and shared many traits with that of Palaeopropithecus. The arms were longer than the legs, but no hand or foot bones have been found for comparison with the other sloth lemurs. Size estimates based on the limited remains have varied widely, ranging as high as 244 kilograms (538 pounds), but the most thorough statistical investigation using regression analyses predicts a mass of 160kg (350lb).
Misattributions and limited remains have resulted in varying opinions about the way Archaeoindris moved in its environment, ranging from tree-dwelling to ground-dwelling. Its skeleton suggests it was a deliberate climber that visited the ground to travel.
The generic name Archaeoindris, meaning "ancient indri-like lemur", is derived from the Greek word ἀρχαῖος (archaios, or "ancient") and indris, a common variation of the generic name Indri.[3] The species name, fontoynontii (sometimes spelled fontoynonti), was selected in honor of Antoine Maurice Fontoynont, the president of the Académie Malgache (Malagasy Academy) at the time. Fontoynont was reported to have been supervising the excavation when it was discovered.[4]
Evolutionary history
Archaeoindris was a type of sloth lemur (family Palaeopropithecidae), a recently extinct family of giant lemurs (known as subfossil lemurs) native to Madagascar. Its ancestors were likely arboreal (tree-dwelling), and this giant sloth lemur has been compared to the extinct giant ground sloths of North and South America.[5]
Phylogeny of Archaeoindris and its closest lemur relatives[6][7]
Archaeoindris was most closely related to Palaeopropithecus,[1] a genus containing the second largest of the sloth lemurs and specialized for suspensory behavior in its arboreal habitat.[8] Traits of the postcranium (skeleton below the skull) indicate that Babakotia was the next most closely related sloth lemur to Archaeoindris and Palaeopropithecus, followed by Mesopropithecus,[1] the smallest of the sloth lemurs.[9]
All four genera of sloth lemurs are known to be a sister taxon (close relatives) of family Indriidae, which includes the indri (Indri), sifakas (Propithecus), and woolly lemurs (Avahi). This relationship is supported by data from morphological, developmental, and molecular research. Another member of this clade (related group) is the family of monkey lemurs (Archaeolemuridae). Dental features, such as the morphology of their molar teeth and the modified number of teeth in their toothcomb (a specialized grooming structure found in lemuriforms), have long suggested a relationship.
However, other anatomical and developmental traits suggested that monkey lemurs might be more closely related to family Lemuridae, which include five genera of lemur, including the ring-tailed lemur (Lemur catta). Molecular analysis has shown strong support for the former, placing the monkey lemurs in a clade with the sloth lemurs and indriids.[1]
Taxonomic classification
The family Palaeopropithecidae contained a large number of species compared to most other subfossil lemur families. It included four known genera and seven species, all of which are now extinct.[10] Among these was the genus Archaeoindris, one of only a few monotypic lemur taxa.[11]
Archaeoindris fontoynontii was first described by Herbert F. Standing in 1909 from two fragments of a maxilla (upper jaw) and a complete mandible (lower jaw).[12][13] These type specimens—AM-6239 (maxillae) and AM-6237 (mandible)—are stored in the collection at the University of Antananarivo.[14] The mandible contains a complete set of upper teeth, the left maxillary fragment contains the last premolar (P4) and all three molars (M1–M3), and the right maxillary fragment bears both premolars (P2 and P4) and the first molar (M1).[13]
At the time, Standing noted similarities with the dentition of Palaeopropithecus. Sixteen years after Standing's discovery, Charles Lamberton discovered the first and only complete cranium (skull) and associated mandible for Archaeoindris, both of which were well preserved. He published this find in 1934.[13]
Only six postcranial specimens of Archaeoindris have been found. Two of these belonged to an adult and include a damaged humerus (upper arm bone) and an almost complete femur (thigh bone). The other four come from an immature individual and include a damaged humerus, a damaged ulna (lower arm bone), and two femurs, both lacking the epiphyses (rounded end of the bone) on both ends.
Archaeoindris is one of the least common of the subfossil lemurs, and the few known specimens were all found at Ampasambazimba in the Central Highlands.[12] Excavations run by a multi-disciplinary Malagasy-American team at this fossil site between 1983 and 1984 yielded no new subfossil remains, and no other potential sites are known for this species.[15]
Historically, some remains from other subfossil lemurs have been mistakenly attributed to Archaeoindris, resulting in incorrect interpretations of its anatomy and behavior.[12] In 1934, Lamberton missed earlier attribution errors[16] and incorrectly labeled a tibia and two fibulae (lower leg bones) from a species of koala lemur (Megaladapis grandidieri) as belonging to Archaeoindris. Because of these misattributions and Lamberton's use of the immature bones, his reconstruction was inaccurate.[12][17]
In 1936, Alice Carleton corrected Lamberton by identifying the tibia and fibulae as belonging to a koala lemur. Carleton's corrections were later confirmed and other misattributions were corrected in the 1960s and 1970s by Alan Walker and William L. Jungers.[12][18]
In 1910, twenty-four years before Lamberton's monograph on Archaeoindris, Standing identified a massive right femur from Ampasambazimba as a new species, Lemuridotherium madagascariense. Although Standing recognized the strong similarities between Lemuridotherium and Archaeoindris, he placed them in separate genera due to what he perceived as a great size difference.[18] Lamberton was also persuaded by the size difference, partly because he failed to recognize the smaller tibia and fibulae as belonging to the smaller Megaladapis grandidieri. Furthermore, Lamberton did not realize that the smaller femurs he assigned to Archaeoindris belonged to a juvenile.[19]
Although some later authors considered Lemuridotherium a synonym of Archaeoindris, it was not until 1988 that Martine Vuillaume-Randriamanantena provided a definitive proof.[18] Vuillaume-Randriamanantena also established associations between the postcrania and crania of Archaeoindris,[16] summarized what is known about the postcranial skeleton, and documented the strong similarity with the genus Palaeopropithecus.[12]
Anatomy and physiology
Though similar to Palaeopropithecus, Archaeoindris was significantly larger and more robust.[5][14]Archaeoindris was one of the largest primates to ever evolve,[10] and was the largest-known strepsirrhine primate,[13] weighing an estimated 160kg (350lb).[2] It was roughly the size of an adult male gorilla,[12] which was first noted by Lamberton.[20]
Since its discovery, size estimates have varied from "larger than a human" to "possibly the largest primate ever". In a study by Jungers from 1990, the area of its molar teeth predicted a mass of 230.5kg (508lb), while the femoral head diameter predicted a mass of 244.1kg (538lb).[20] In 1995, Laurie Godfrey estimated a mass of 197.5kg (435lb) using the midshaft circumferences of the humerus and femur.[21] Using multiple regressions of the cortical area of the femur in 2008,[22] Jungers and colleagues generated the current best estimate of 161.2kg (355lb) with a possible range of 150–187.8kg (331–414lb).[23] These estimates were considered to be more accurate since the harder cortical bone in the midshaft of the femur supported an animal's weight, and its thickness better correlated with the animal's mass than the midshaft diameter (which includes both hard cortex and spongy bone).[21] The only fossil primate that was probably larger than Archaeoindris was Gigantopithecus blacki, a close relative of orangutans.[24]
Like all three species of Palaeopropithecus, Archaeoindris exhibited derived traits not seen in the two other less specialized genera of sloth lemur.[7] These traits included deflated auditory bullae and paired protrusions of bone around the nasal opening consisting of part of the premaxilla and the nasal bones.[14][25][26] Its skull was wider than that of Megaladapis, but shorter, measuring 269 millimeters (10.6 inches).[2] Its face was shorter than that of Palaeopropithecus,[5] with its eyes directed further forward. The neurocranium (braincase) was small[2] and elevated relative to the face, unlike Palaeopropithecus.[27]Postorbital constriction (narrowing of the skull behind the eye sockets) is pronounced.[2] The skull also bore a low, broad sagittal crest (a ridge of bone on the top of the skull to which jaw muscles attach) and robust but smaller nuchal crests (ridges of bone on the back of the skull to which neck muscles attach).[2][5][27]
The rims of the orbits (eye sockets) were not as thick as those of Palaeopropithecus.[25] The area of the orbit was 946mm2 (1.466sqin), comparable to that of gorillas. The ratio of its orbit area to the size of its optic canal indicates that Archaeoindris had low retinal summation, meaning its eyes were as sensitive to light as those of living diurnal lemurs. Yet the ratio was not as low as in comparably sized apes, suggesting Archaeoindris had lower visual acuity than apes do and lacked trichromatic color vision.[28]
Mandible and fragmentary maxillae of A. fontoynontii (1909)
The jaw exhibited a long, robust mandibular symphysis (joining of the two halves of the lower jaw), which fused early during development.[25][29] Its palate (bones on the roof of the mouth) was rectangular.[14] Like other sloth lemurs, it likely experienced accelerated dental development,[29] and had an adult dental formula of 2.1.2.32.0.2.3.[26] Its teeth were also similar to those of Palaeopropithecus, both in morphology and proportions.[2] The four lower incisors that would have made up the toothcomb were modified, being shorter and more robust, possibly for feeding purposes.[30] The canines were short and stout, but sharp.[31] Also, there was a diastema (gap) between the lower premolars (p2 and p4). Other dental similarities with Palaeopropithecus included small third upper and lower molars (M3 and m3), the first and second molars were narrow and long, and the enamel of its cheek teeth was crenulated (low and rounded), though not as wrinkled and slightly higher-crowned.[2]
Most bones of the postcranial skeleton, including the bones of the hands, feet, vertebral column, ribs, radius (lower arm bone), tibia, and fibula, have not been found for Archaeoindris.[32] As with many cranial features, the postcranial bones that have been discovered are similar to that of Palaeopropithecus, but significantly larger and more robust. The head of the femur was large and lacked a fovea capitis femoris (a small depression in the head of the femur).[2] The femur was short and extremely robust,[14] had a very high collodiaphyseal angle (the angle of the neck and shaft of the bone), and the greater trochanter was small.[2]
In the adult, the humerus was significantly longer than the femur, while in the immature specimen, both the humerus and ulna were much longer than the femur,[33] making the arms considerably longer than the legs, as also seen in Palaeopropithecus. Yet, the relative length of arms to legs was shorter in Archaeoindris, so although its intermembral index was over 100, it was lower than that of Palaeopropithecus.[2][34]
Behavior
Life restoration of Archaeoindris fontoynontii
Archaeoindris is thought to have been a leaf-eater (folivorous),[5] a view supported by wear patterns on its teeth.[35] Its fused mandibular symphyses and the likelihood of accelerated dental development suggest that it began processing fibrous foods in the mouth with thorough chewing.[29] Its diet may also have included some fruits and seeds.[36] Like most of the other giant lemurs, Archaeoindris is thought to have been diurnal because of its relatively small orbits, which are comparable to those of gorillas.[37]
Both Standing and Lamberton assumed Archaeoindris to be a slow-moving tree-dweller like Megaladapis, primarily due to the misattributed bones. Lamberton also speculated that it would have resembled a ground sloth—a view later supported by Jungers in 1980 after several misattributions had been corrected and having considered its gorilla-like size. Jungers went on to propose that it would have spent most of its time on the ground (terrestrial).
However, the functional morphology of its hip joint indicates a degree of mobility typically seen in more arboreal animals.[33] Other traits shared with Palaeopropithecus, particularly seen in the femur, suggest that Archaeoindris spent considerable time in the trees for feeding and possibly nesting,[25][38] although it also would have visited the ground to feed and travel. It is described as a deliberate, scansorial (climbing) browser, and it is unknown whether it was like Palaeopropithecus in performing hang-feeding since hand and foot bones are missing. Given its bulky size, this would be unexpected.[33]
Distribution and habitat
Archaeoindris is known from only one subfossil site, Ampasambazimba, in central Madagascar, and all remains date to the Late Quaternary.[39] The area today is dominated by grasslands, particularly of the grass genus Aristida.[40] Prior to human arrival, the area around Ampasambazimba was not completely forested, but more of an open habitat, consisting of a mix of woodlands, bushlands, and savanna.[41] Animal remains at this subfossil site have yielded about 20 species of lemur living in sympatry (sharing the same geographic area). In comparison, the nearby Ambohitantely Special Reserve today contains only four species, roughly 20% of the area's original lemur diversity.[42]
Extinction
Despite being the most species-rich family among the giant lemurs, all four genera of sloth lemur, including Archaeoindris, have gone extinct.[35]Radiocarbon dating of the stratigraphic level of some of the Archaeoindris remains were dated to 8000BP,[5] while two other specimens were dated to 2362–2149BP (412–199BCE) and 2711–2338BP (761–388BCE).[43] From these dates, it is likely that Archaeoindris was still alive on the high plateau in 350BCE when the first humans reached the west coast of Madagascar,[44] despite being rare by that time. Consequently, it would have been especially vulnerable to hunting and habitat loss.[5]
Related Research Articles
Megaladapis, informally known as the koala lemur, is an extinct genus of lemurs belonging to the family Megaladapidae, consisting of three species that once inhabited the island of Madagascar. The largest measured between 1.3 to 1.5 m in length.
Plesiorycteropus, also known as the bibymalagasy or Malagasy aardvark, is a recently extinct genus of mammals from Madagascar. Upon its description in 1895, it was classified with the aardvark, but more recent molecular evidence instead suggests that it is most closely related to the tenrecs. Two species are currently recognized, the larger P. madagascariensis and the smaller P. germainepetterae. They probably overlapped in distribution, as subfossil remains of both species have been found in the same site.
Palaeopropithecus is a recently extinct genus of large sloth lemurs from Madagascar related to living lemur species found there today. Three species are known, Palaeopropithecus ingens, P. maximus, and P. kelyus. Radiocarbon dates indicate that they may have survived until around 1300–1620 CE. Malagasy legends of the tretretretre or tratratratra are thought to refer to P. ingens.
Mullerornis modestus is an extinct species of elephant bird, and the only member of the genus Mullerornis.
Cryptoprocta spelea, also known as the giant fossa, is an extinct species of carnivore from Madagascar in the family Eupleridae which is most closely related to the mongooses and includes all Malagasy carnivorans.
The monkey lemurs or baboon lemurs (Archaeolemuridae) are a recently extinct family of lemurs known from skeletal remains from sites on Madagascar dated to 1000 to 3000 years ago.
The sloth lemurs (Palaeopropithecidae) comprise an extinct family of lemurs that includes four genera. The common name can be misleading, as members of Palaeopropithecidae were not closely related to sloths. This clade has been dubbed the ‘‘sloth lemurs’’ because of remarkable postcranial convergences with South American sloths. Despite postcranial similarities, the hands and feet show significant differences. Sloths possess long, curved claws, while sloth lemurs have short, flat nails on their distal phalanges like most primates.
Archaeolemur is an extinct genus of subfossil lemurs known from the Quaternary of Madagascar. Archaeolemur is one of the most common and well-known of the extinct giant lemurs as hundreds of its bones have been discovered in fossil deposits across the island. It was larger than any extant lemur, with a body mass of approximately 18.2–26.5 kg (40–58 lb), and is commonly reconstructed as the most frugivorous and terrestrial of the fossil Malagasy primates. Colloquially known as a "monkey lemur," Archaeolemur has often been compared with anthropoids, specifically the cercopithecines, due to various morphological convergences. In fact, it was even misidentified as a monkey when remains were first discovered. Following human arrival to Madagascar just over 2000 years ago, many of the island’s megafauna went extinct, including the giant lemurs. Radiocarbon dating indicates that Archaeolemur survived on Madagascar until at least 1040-1290 AD, outliving most other subfossil lemurs.
Pachylemur is an extinct, giant lemur most closely related to the ruffed lemurs of genus Varecia. Two species are known, Pachylemur insignis and Pachylemur jullyi, although there is some doubt as to whether or not they may actually be the same species. Pachylemur is sometimes referred to as the giant ruffed lemur, because although it and the living ruffed lemurs had similar teeth and skeletons, Pachylemur was more robust and as much as three to four times larger. DNA studies have confirmed a sister group relationship between these two types of lemur. Like living ruffed lemurs, Pachylemur specialized in eating fruit, and was therefore an important seed disperser, possibly for tree species with seeds too large for even ruffed lemurs to swallow. In the spiny thickets of southwestern Madagascar, they were also likely to have dispersed seeds evolved to attach to fur and be carried away. Unlike ruffed lemurs, the fore- and hindlimbs of Pachylemur were nearly the same length, and therefore it was likely to be a slow, deliberate climber. However, both used hindlimb suspension to reach fruit on small branches below them.
Hadropithecus is a medium-sized, extinct genus of lemur, or strepsirrhine primate, from Madagascar that includes a single species, Hadropithecus stenognathus. Due to its rarity and lack of sufficient skeletal remains, it is one of the least understood of the extinct lemurs. Both it and Archaeolemur are collectively known as "monkey lemurs" or "baboon lemurs" due to body plans and dentition that suggest a terrestrial lifestyle and a diet similar to that of modern baboons. Hadropithecus had extended molars and a short, powerful jaw, suggesting that it was both a grazer and a seed predator.
Babakotia is an extinct genus of medium-sized lemur, or strepsirrhine primate, from Madagascar that contains a single species, Babakotia radofilai. Together with Palaeopropithecus, Archaeoindris, and Mesopropithecus, it forms the family Palaeopropithecidae, commonly known as the sloth lemurs. The name Babakotia comes from the Malagasy name for the indri, babakoto, to which it and all other sloth lemurs are closely related. Due to its mix of morphological traits that show intermediate stages between the slow-moving smaller sloth lemurs and the suspensory large sloth lemurs, it has helped determine the relationship between both groups and the closely related and extinct monkey lemurs.
Mesopropithecus is an extinct genus of small to medium-sized lemur, or strepsirrhine primate, from Madagascar that includes three species, M. dolichobrachion, M. globiceps, and M. pithecoides. Together with Palaeopropithecus, Archaeoindris, and Babakotia, it is part of the sloth lemur family (Palaeopropithecidae). Once thought to be an indriid because its skull is similar to that of living sifakas, a recently discovered postcranial skeleton shows Mesopropithecus had longer forelimbs than hindlimbs—a distinctive trait shared by sloth lemurs but not by indriids. However, as it had the shortest forelimbs of all sloth lemurs, it is thought that Mesopropithecus was more quadrupedal and did not use suspension as much as the other sloth lemurs.
Hypogeomys australis is an extinct rodent from central and southeastern Madagascar. First described in 1903, it is larger than its close relative, the living Hypogeomys antimena, which occurs further west, but otherwise similar. Average length of the femur is 72.1 mm, compared to 63.8 mm in H. antimena. One of the few extinct rodents of Madagascar, it survived to at least around 1536 BP based on radiocarbon dating. Little is known of its ecology, but it may have lived in burrows like its living relative and eaten some arid-adapted plants.
Subfossil lemurs are lemurs from Madagascar that are represented by recent (subfossil) remains dating from nearly 26,000 years ago to approximately 560 years ago. They include both extant and extinct species, although the term more frequently refers to the extinct giant lemurs. The diversity of subfossil lemur communities was greater than that of present-day lemur communities, ranging to as high as 20 or more species per location, compared with 10 to 12 species today. Extinct species are estimated to have ranged in size from slightly over 10 kg (22 lb) to roughly 160 kg (350 lb). Even the subfossil remains of living species are larger and more robust than the skeletal remains of modern specimens. The subfossil sites found around most of the island demonstrate that most giant lemurs had wide distributions and that ranges of living species have contracted significantly since the arrival of humans.
Lemurs were first classified in 1758 by Carl Linnaeus, and the taxonomy remains controversial today, with approximately 70 to 100 species and subspecies recognized, depending on how the term "species" is defined. Having undergone their own independent evolution on Madagascar, lemurs have diversified to fill many ecological niches normally filled by other types of mammals. They include the smallest primates in the world, and once included some of the largest. Since the arrival of humans approximately 2,000 years ago, lemurs have become restricted to 10% of the island, or approximately 60,000 square kilometers (23,000 sq mi), and many face extinction. Concerns over lemur conservation have affected lemur taxonomy, since distinct species receive increased conservation attention compared to subspecies.
Charles Lamberton was a French paleontologist who lived and studied on the island of Madagascar between 1911 and 1948 and specialized in the recently extinct subfossil lemurs. He made significant contributions towards fixing misattributions of skeletal remains and poor interpretations of subfossil lemur behavior. His paleontological expeditions during the 1930s led to the discovery of a new species of Mesopropithecus, a type of sloth lemur. Three species—one mammal and two reptiles—were named after him, although one is now considered a taxonomic synonym.
Herbert Fox Standing was an English paleontologist and Quaker medical missionary in Madagascar. He was the author of the book The Children of Madagascar (1887) and the Headmaster of the Boys' High School of the Friends' Foreign Mission Association in Antananarivo.
Ampasambazimba is a mountain peak and subfossil site in Madagascar, near Analavory, (Itasy) most known for being the site of the remains of the extinct giant sloth lemur Archaeoindris.
Godfrey, L. R.; Jungers, W. L. (2003a). "Subfossil Lemurs". In Goodman, S. M.; Benstead, J. P (eds.). The Natural History of Madagascar. University of Chicago Press. pp.1247–1252. ISBN978-0-226-30306-2.
MacPhee, R. D. E.; Burney, D. A.; Wells, N. A. (1985). "Early Holocene chronology and environment of Ampasambazimba, A Malagasy subfossil lemur site". International Journal of Primatology. 6 (5): 463–489. doi:10.1007/BF02735571. S2CID44449535.
Vuillaume-Randriamanantena, M. (1988). "The taxonomic attributions of giant subfossil lemur bones from Ampasambazimba: Archaeoindris and Lemuridotherium". Journal of Human Evolution. 17 (4): 379–391. Bibcode:1988JHumE..17..379V. doi:10.1016/0047-2484(88)90027-9.
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